Systems are known for counting blood cells or other particles suspended in a liquid, a preferred system being shown in U.S. Pat. No. Re. 27,902 assigned to the assignee of the present invention. In such a system, electrical pulses are provided in response to the passage of particles through a metering aperture of a transducer or conductivity cell which is disposed within a fluid path and which has electrodes on respective opposite sides of the aperture. The impedance of the fluid path is materially altered by the presence of a particle within the aperture, resulting in production of electrical pulses corresponding to the number of particles passing through the aperture and which pulses are electronically counted to provide an output indication of particle count. A known volume of particle-containing liquid is usually metered by appropriate means to provide a particle count for a known volume of liquid.
Such systems are often employed for counting platelets within a suitably diluted platelet sample. The platelet count is subject to coincidence error which arises by reason of the coincident or nearly coincident passage of more than one particle through the metering aperture of the conductivity cell and which is sensed as a single particle, resulting in the number of measured particles being lower than the actual particle count for a given quantity of sample liquid. The platelet count is also dependent upon measured hematocrit value. Correction charts are usually employed to provide a corrected platelet count. It would be preferable however to employ automated means to directly provide a corrected platelet count to thereby overcome the time and susceptibility to error occasioned by the usual manual use of correction charts.